Income Tax losses
An individual who is trading may be able to reduce their Income Tax liability by offsetting any losses from their trade against future profits or other income. HMRC’s Losses: HS227 Self Assessment helpsheet has more information (including restrictions that apply).
If profits from activities are taxable as miscellaneous income, losses may be able to be carried forward to later years. More information on this can be found in helpsheet HS325: other taxable income.
https://www.gov.uk/government/publications/tax-on-cryptoassets/cryptoassets-for-individualsNew clarification by uk gov, quite imporant I'd say.
If you invested in 2017 and got loss, you may pay less tax on your earnings.